This invention relates to an apparatus for flattening irregular circumferential surfaces in spirally formed pipes, and an apparatus for cutting such pipes.
As discussed in my U.S. Pat. No. 4,823,579, issued Apr. 25, 1989, and my U.S. Pat. No. 4,567,742, issued Feb. 4, 1986, there are many ways to form a pipe by spirally winding a continuous strip of metal. My U.S. Pat. No. 4,567,742 describes a machine which starts with a flat strip of metal. The strip passes through a series of rollers which bend the edges into predetermined shapes, and form parallel corrugations in the strip. The strip then passes around the inner surface of the forming head in a spiral manner, so that the strip takes a spiral shape with opposite edges of the strip meshing. The intermeshed edges of the strip are then compressed to form the pipe with a spiral lockseam. The strip is continuously fed into the machine to continuously produce spiral pipe. The spirally formed pipe moves away from the forming head in the axial direction of the pipe and rotates.
At some point, the pipe will reach its desired length and must be cut. In the past, a rotary saw was used for cutting the pipe. There are many disadvantages to using a rotary saw to cut metal pipes. First, the saw blade, rotating as fast as 5000 RPM, is dangerous to the machine operator and anyone near the machine. Second, the saw generates a lot of sparks when it cuts the metal, which also creates a hazardous situation. Third, the saw cut leaves burrs on the edge of the pipe. These burrs must be filed off in a secondary operation, which increases pipe production costs. Finally the cutting operation generates high noise levels.
My pending U.S. patent application Ser. No. 07/315,373, filed Feb. 23, 1989, discloses a cutting apparatus for hollow metal pipes that overcomes the disadvantages of high speed saw blades. In that apparatus, a first rotatable knife is positioned inside the spiral pipe, a second rotatable knife is positioned outside of the pipe, and a support roller is positioned outside the pipe and opposite the outer knife. To cut the pipe, the outer knife is moved into an overlapping relationship with the inner knife, and the support roller is moved into contact with the pipe. The overlapping knives and support rollers move axially with the pipe and cooperate to cut the pipe as the pipe move axially and rotates between the overlapping inner and outer knifes.
The pipe cutting apparatus of my U.S. patent application Ser. No. 07/315,373, described above, uses a slitter-type shearing action to cut the pipe. The pipe is cut without the sparks, noise, and danger of a high-speed saw blade. Thus, this apparatus provides a safer environment for manufacturing spiral seamed pipe.
The above described cutting apparatus of my pending U.S. patent application Ser. No. 07/315,373 worked satisfactorily when the spiral pipes were formed from flat strips of metal having a flat surface configuration. With a flat strip of metal the spiral pipe forming apparatus would create a pipe with a relatively smooth inside and outside circumferential surface which the rotating knives could cut cleanly with a minimum of material burring or deformation to the circular cross section of the pipe.
But often it is necessary to use metal strips having various non-flat surface configurations for different spiral pipe applications. For example, fluting, louvers, or corrugations may be required in the spiral pipe surface. Also, when multiple perforations are required in the spiral pipe, it may be preferred to punch the perforations in the metal strip during the pipe forming process using the drive rollers of the forming apparatus. The punching of perforations in the metal by the drive rollers during the forming process is less expensive than using pre-perforated, flat metal strip. But the punching process deforms the metal strip sheet around the perforated area creating raised surface irregularities.
With the above types of non-flat surface configurations, the cutting apparatus of my previous invention sometimes would not cut a clean edge on the formed spiral pipe. The rotating knife assembly would deform the irregular circumferential pipe surface during the rotating cutting process, sometimes resulting in a rough, non-uniform cut. Also, because of the non-flat surface configurations in the material and deformation during the cutting of the pipe, the ends of the pipe would often not have a smooth and circular inside and outside surface at the cut. A smooth, circular cross-section at the pipe end is often a necessity for proper mating of the pipe with other components in an end use application.